Communication systems transport data from a transmitter to a receiver over a data link. Before transmission, data may be encoded in analog or digital formats. Some communication systems may modulate a carrier signal to carry the data information from the transmitter to the receiver. At the receiver, data may be recovered by demodulating the received signal.
Data links that transport data may be wired or wireless. Wired communication systems may include telephone networks, cable television, internet service provider, and fiber-optic communication nodes, for example. Wireless data links may transfer information between two or more points that are not connected by an electrical conductor. Wireless data links may transport data by using electromagnetic waves propagating through a medium, such as air or free space. Some wireless links may transport information in the form of light.
At a receiver in a digital communication system, a digitally-encoded data stream may be received as an analog signal and converted to a digital format by an analog-to-digital converter (ADC). The ADC interprets the data stream as a function of time. For example, some ADCs may be synchronized to a clock signal that determines when a voltage signal is to be sampled.